(1) Field of the Invention
The invention relates to a method of cleaning an integrated circuit and more particularly, to a method of cleaning an integrated circuit so as to remove particles contaminating said integrated circuit.
(2) Description of the Prior Art
In the manufacture of integrated circuits, it is necessary to remove silicon and silicon oxide at various stages of the fabrication process, especially after wafers have gone through a hydrofluoric acid etching process. The standard method of removal is illustrated by the process flow in FIG. 1. Step 1 is immersion in hydrofluoric acid wherein the silicon oxide is etched away. This is followed by a quick dump rinse, 2, in de-ionized water followed by a spin dry, 3.
The problem with this method is that unwanted particles remain on the wafer. Many of these particles may be the result of the interaction of the silicon with the hydrofluoric acid. When the wafer is immersed in the hydrofluoric acid, silicon hydride is formed which absorbs particles. Silicon hydride formed on the wafer surface may also attract particles. Particles can be picked up from the hydrofluoric acid tank.
Workers in the field generally use the removal process illustrated in FIG. 2. The first three steps of the original process are used. Step 1 is the hydrofluoric acid immersion, followed by step 2--quick dump rinse with de-ionized water, and step 3--spin dry. Step 4 is a high temperature RCA 1 clean. This is usually a solution of ammonium hydroxide--hydrogen peroxide at more than 75.degree. C. The wafers are typically immersed in the solution for about 10 minutes. The high temperature is required to break the chemical bonds which have been formed between the silicon wafer and the particles. A second quick dump rinse, 5, and spin dry, 6, complete the removal process. The article "Developing Contamination-Free Cleaning and Drying Technologies," (Tadahiro Ohmi, Hiroyuki Mishima, Tetsuo Mizuniwa, and Mitsuo Abe in Microcontamination, May 1989, pp. 25-32,108) discusses such an ammonia-hydrogen peroxide RCA cleaning system. These processes still result in particle counts which are too high.